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13 Dec 2019

3. Calculate the pH values of the following aqueous solutions respectively:

(1): 0.01 M HCl solution (stomach acid).

(2): 0.01 M HCOOH (an ingredient from Texas fire ants, formic acid, K_{a(formic acid)} = 2.1x10^-4, similar to HAc)

(3): 0.01 M NaOH.

(4): 0.01 M NaCl.

(5): 1x10^-9 M [H⁺]

(6): 0.01 M NH₃ (K_b(ammonia) = 5.0x10^-10 ) (A challenged problem):

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1) What is the pH (to nearest 0.01 pH unit) of a solution prepared by mixing 90.0 mL of 0.0509 M NaOH and 60.0 mL of 0.0400 M Ba(OH)2?

2) What is the pH (to nearest 0.01 pH unit) of a solution prepared by mixing 78.0 mL of 0.604 M HCl and 69.0 mL of 0.823 M NaOH?

3) Calculate the pH of each of the solutions and the change in pH to 0.01 pH units caused by adding 10.0 mL of 2.54-M HCl to 470. mL of each of the following solutions.

Change is defined as final minus initial, so if the pH drops upon mixing the change is negative.

a) water

pH before mixing =
pH after mixing=
pH change =

b) 0.178 M C₂H₃O₂^1-

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pH after mixing=
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c) 0.178 M HC₂H₃O₂

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pH after mixing=
pH change =

d) a buffer solution that is 0.178 M in each C₂H₃O₂^1- and HC₂H₃O₂

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4) Calculate the change in pH to 0.01 pH units caused by adding 10. mL of 2.60-M NaOH is added to 550. mL of each of the following solutions.

a) water

pH before mixing =
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b) 0.176 M NH₄¹⁺

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pH after mixing=
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c) 0.176 M NH₃

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d) a buffer solution that is 0.176 M in each NH₄¹⁺ and NH₃

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Consider the titration of 30.0 mL of 0.189-M of KX with 0.172-M HCl. The pK_a of HX = 8.59. Give all pH values to 0.01 pH units.

a) What is the pH of the original solution before addition of any acid?

pH =

b) How many mL of acid are required to reach the equivalence point?

V_A = mL

c) What is the pH at the equivalence point?

pH =

d) What is the pH of the solution after the addition of 11.2 mL of acid?

pH =

e) What is the pH of the solution after the addition of 39.6 mL of acid?

pH =

A 4.543-g sample of a solid, weak, monoprotic acid is used to make 100.0 mL of solution. 15.0 mL of this solution was titrated with 0.07921-M NaOH. The pH after the addition of 28.38 mL of base was 5.60, and the equivalence point was reached with the addition of 48.60 mL of base.

a) How many millimoles of acid are in the original solid sample? Hint: Don't forget the dilution.

mmol acid

b) What is the molar mass of the acid?

g/mol

c) What is the pK_a of the acid?

pK_a =

A lot of these are similar problems, so if someone could let me know how to do them then I could probably figure the rest of them out. I was out of class the day we went over this and am completely lost.

1)Calculate the pH of a solution that results from mixing 10 mL of 0.11 M ammonia with 39 mL of 0.11 M ammonium chloride. The K_b value for NH₃ is 1.8 x 10^-5

2)A buffer that contains 0.18 M of an acid, HA and 0.31 M of its conjugate base A^-, has a pH of 4.66. What is the pH after 0.034 mol of HCl are added to 0.6 L of the solution

3)Calculate the pH during the titration of 30.00 mL of 0.1000 M NaOH(aq) with 0.1000 M HNO₃(aq) after 12 mL of the acid have been added

4)Calculate the pH during the titration of 20.00 mL of 0.1000 M HBrO(aq) with 0.1000 M LiOH(aq) after 8 mL of the base have been added. K_a of hypobromous acid = 2.3 x 10^-9.

5)Calculate the pH during the titration of 20.00 mL of 0.1000 M methylamine, (CH₃)NH₂(aq), with 0.2000 M HCl(aq) after 7.5 mL of the acid have been added. K_b of methylamine = 3.6 x 10^-4

6)Calculate the pH during the titration of 30.00 mL of 0.1000 M dimethylamine, (CH₃)₂NH(aq), with 0.1000 M HBr(aq) after 29 mL of the acid have been added. K_b of dimethylamine = 5.4 x 10^-4

⁷⁾Determine the volume in mL of 0.2 M HCl(aq) needed to reach the equivalence (stoichiometric) point in the titration of 49 mL of 0.25 M NH₂NH₂(aq)(aq). The K_b of hydrazine is 1.7 x 10^-6

⁸⁾Determine the pH at the equivalence (stoichiometric) point in the titration of 23 mL of 0.12 M C₆H₅COOH(aq) with 0.22 M NaOH(aq). The K_a of benzoic acid is 6.5 x 10^-5

what is the pH of a solution after titrating 50.0 mL of 0.650 pyridine, C₅H₅N (K_b = 1.8x10^-9), with 50.0 mL of HCl?

a. 4.47 b. 2.71 c. 5.74 d. 2.87 e. 5.43

____________________________________________

a 10.0 mL sample of 0.75 M CH₃CH₂CO₂H (ka1=1.3x10^-5) is titrated with 0.30 M NaOH. what is the pH of the solution after 22.0 mL of NaOH have been added to the acid?

a. 4.89 b. 5.00 c. 5.75 d. 4.12 e. 2.50

___________________________________________

what is the pH of a solution prepared with 0.50 M HC3H5O3 (lactic acid) (Ka1 = 1.4x10^-4) and 0.75 M NaC3H5O3 (sodium lactate)?

a. 0.46 b. 2.00 c. 3.68 d. 4.03 e. 3.85

__________________________________________

calculate the solubility of sliver chromate , Ag2CrO4 (Ksp=1.1x10^-12), in 0.005 M Na2CRO4.

a. 3.4x10^-5 b. 1.0x10^-6 c. 8.2x10^-5 d. 5.2x10^-7 e. 7.4x10^-6

___________________________________________

If the solubility of barium fluoride is 7.2x10^-3 M, what is the Ksp of BaF₂?

a. 7.5x10^-7 b. 3.7x10^-7 c. 7.2x10^-3 d. 1.5x10^-6 e. 5.2x10^-5

_________________________________________

which of the following aqueous mixtures would be a buffer system?

a. NH3(Kb=1.8x10^-5), NaOH

b. H2SO4(Ka1=very large)(Ka2=1.2x10^-2), CH3COOH(Ka1=1.8x10^-5)

c. H3PO4(Ka1=7.5x10^-3)(Ka2=6.2s10^-8)(Ka3=4.8x10^-13), NaH2PO4

d. HCl, NaCl

e. HNO3,NaNO3

___________________________________________

How many grams of NaOBr should be added to 50.0 mL of 0.650 M of HOBr(Ka1=2.0x10^-9) to make a buffer at pH 8.90

a. 123

b. 6.12

c. 8.70

d. 1.03

e. 1.58

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